Forming hollow blanks

ABSTRACT

A hollow blank is slipped on a punch to be formed in cooperation with a die. Prior to engagement with the die, the blank is held and retained on the punch in a manner which does not disturb the forming process.

United States Patent Kienzler et al. 14 1 June 20, 1972 [541 FORMING HOLLOW BLANKS 159.1 7, 9 References qua [72] Inventors: Wolfgang Klenzler, Numberg; Marten UNITED STATES PATENTS Burgdorf, Schwaig, both of Germany 3,516,274 6/1970 Grahm et a1. ..72/57 Assign: Kabehmd Me erke Gutehom 2,411,082 11/1946 Cont: ..72/348 nungsh m Akfl g fl Haflnovel', FOREIGN PATENTS 0R APPLICATIONS Germany 951,807 11/1956 Germany ..72/57 [22] Filed: Aug. 26, 1970 698,366 11/1940 Germany 255,869 7/1967 Austria 901,766 7/1949 Germany....

[30] Foreign Application Priorlty Dag Primary Examiner-Richard J. Herbst Attorney-Smyth, Roston & Pavitt and Ralf H. Siegemund Aug. 29, 1969 Germany ..P 19 43 884.7

[57] ABSTRACT ..72 347, 72 361 B 8' 22/10 A hollow blank is slipped on a punch to be formed 1n coopera- 58] Fieid of Search 72/343 349 361 tion with a die. Prior to engagement with the die, the blank is held and retained on the punch in a manner which does not 4 .v 1 disturb the forming process.

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: I! I 5 I I I z 1 Can/rd?! Preffure FORMING HOLLOW BLANKS The present invention relates to the art of forming hollow blanks, such as drawing or squeezing tubes or cups. More particularly, the invention relates to metal working equipment wherein a die member coacts with a punch for obtaining plastic deformation of a hollow blank. The die member is usually a stationary part of the machine and has an aperture or die cavity which determines outer dimensions and contour of the final product; the punch is held on a movable ram or plunger and detennines the inner dimensions and contour of the part to be formed.

In cases, a cylindrical hollow blank, such as a cup or tube, is placed manually or by means of feeder equipment into the receiving cavity of the forming tool such as the die cavity. This method of loading the tool is usually employed for direct as well as for inverted extrusion, and also for drawing blanks into an axially symmetrical product. The clearance between die cavity and outer diameter of the blank is selected so that the punch enters the blank with certainty.

However, the blank cannot always be placed into the mold or die prior to working, in more or less random position. This will particularly be the case if the inner contour of the blank is not circular; for example, the inner cross section may be quadrilateral or hexagonal. As the punch has matching contour, it is necessary to orient the blank angularly, in relation to the axis defining the direction of punch movement during working, so that the punch may enter the hollow blank in contour fitting relationship.

An apparent solution to the problem of proper orientation is to provide the outer surface of the blank with a fitting or indexing area, there being a matching indexing surface area in the die cavity. Thus, the blank can be placed into the die in a particular indexed position only, and in that position it is properly oriented to the punch. Also, turning of the blank out of the indexed position may be prevented through suitable choice of the indexing areas. However, this type of positioning and orienting will not always be satisfactory, particularly because it may not always be possible to establish such indexing surfaces. Moreover, once working has begun, the forces interacting between die, blank and punch change their relation and character. This concerns particularly to reactive forces. Thus, as a result of plastic deformation, the blank may begin to turn in the die rather than react into the die. Also, the inherent asymmetry of the indexing areas may influence the flow pattern of the material, which could be disadvantageous as to unifonnity of the final product.

Holding the blank down in the die cavity or in a particular blank holder prior to the operating stroke of the punch is not possible for a blank that is a cup with a flange, having diameter larger than the diameter of the holder aperture; and if, for example, the material of the flange is to be included in the drawing process.

As placement of a hollow blank into the die in an indexed position or holding the blank down is not practical, it was found necessary to slip the non-circular hollow blank manually onto the correspondingly shaped punch when in a retracted position. However, this procedure is prone to accidents, as the hollow blank has to be held on the punch by hand until the punch has actually reached the die, i.e., until the die assumes the retaining function. However, the operators hand was frequently caught by the machine. Mindful of the danger, the operator usually lets go too early, and the blank may slip off the punch prior to being clamped by the die. The blank may fall uncontrolled into the tool and may assume an unforeseeable position in or on the die cavity, and if the punch is not stopped in time, damage to the tool may result.

The problem solved by the invention is to provide for positioning of a blank in relation to machine tools for plastic deformation without incurring the disadvantages and even out-right dangers outlined abOve. The problem is solved particularly for fonning machines using a punch and a die, by providing the die with holding and retaining means which do not participate nor influence the plastic deforming process.

The holding means is provided directly on the die. Particue larly, the holding means is a counter punch-like retaining plunger traversing the die for coaction with the blank on the punch, but from the outside.

The holding and retaining means move the punch during forward stroke to engage the blank for retaining it on the punch in a manner and at locations where the engagement does not disturb the forming process. In many cases, the blank is a cup, having a bottom that does not or is hardly to be deformed. The holding means provides for retaining engagement of the front end of the punch with the bottom'of the blank.

The blank is slipped onthe punch manually, when the punch is being retracted after the respective preceding operating cycle, usually when in upper dead center position and about to reverse direction of stroke. At that point, the holding means take over to retain the blank on the punch, particularly during punch protraction and prior to but until forming proper begins. During this phase, there is sufiicient time for the operator to move a protecting shield, or the like, between.

machine and himself. Thus, the protective means will be in place when the blank engagesthe die and deforming process begins.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection withjthe accompanying drawings in which:

FIG. 1 is a cross section view of drawing equipment improved in accordance with the preferred embodiment of the invention, using suction to hold a blank on a draw punch;

FIG. 2 is a section view of a portion of a draw punch improved in accordance with a different example of the present invention;

FIG. 3 is a section of another example of the present invention, using holding means that traverse the die cavity;

FIG. 4 illustrates a section view of a cold extrusion equipment using another kind of holding means for retaining a blank on the punch; and

FIG. 5 illustrates a view taken along sectionplane 5-5 in FIG. 4.

Proceeding now to the detailed description of the drawing, in FIG. 1 thereof is illustrated a cup-shaped blank 1, having a flange 11 at its open end, and a bottom 12 on the other end. Cup 1 may have quadrilateral internal cross section. The forming equipment includes a drawing die 2 with die cavity 3, and a draw punch 4 that has also quadrilateral cross section and is mounted on a ram or plunger 5. Draw punch 4 must have cross section to fit into the cup-shaped blank.

In view of the particularly contoured cross section of blank and punch, the blank is required to assume a particular, relative position to the punch. On the other hand, because of its flange, blank 1 cannot be guided in an appropriate blank holder. Thus, cup 1 has to be slipped manually onto punch 2 in proper orientation.

Punch 4 is provided with a central bore 6, terminating in an opening 7 in the front face of the punch, adjacent the bottom of cup 1. A flexible conduit 8 connects to bore 6 near its upper end. The connection is sufficiently far from any portion of the punch that is to participate in the drawing process. The other end of conduit 8 is connected to a suction pump 9.

As punch 4 is inserted in cup 1, the vacuum in bore 6 sucks the bottom of cup 1 against the front face of the punch and holds it there. Thus, position retention is ensured at least until the bottom periphery of the cup 1 hits the edge of die 6. As drawing begins, pump 9 can be turned ofl, as further retaining is not needed when the punch presses the blank through the die. The pump 9 should be turned off when the drawn shell is to be stripped ofi'.

Alternatives are available to retain the punch in the cupshaped blank 1. As shown in FIG. 2, the front end of the punch, denoted here with reference numeral 14, is provided with a magnet is attracting bottom 12 of magnetizable cup 1 for retaining the blank 1 as needed.

The embodiment illustrated in FIG. 3 accommodates a similar, cup-shaped blank 1 as slipped on a draw punch 24 that is not connected to a vacuum device. Instead, a counter punch or retaining plunger 26 is provided to traverse the die cavity 3 and to engage the bottom 12 of blank 1 for holding and retaining same on the punch. Plunger 26 is actually a piston rod extension, there being a piston 27 displaceably positioned in a cylinder 28. A pressure source 29 in communication with cylinder 28 is controlled to retract plunger 26 in synchronism with advance of punch 24 during operation stroke. As punch 24 advances, plunger 26 is retracted to impart sufiicient pressure upon cup 1 for urging same towards the punch without, however, providing punch braking action. Actually, the ram may advance the plunger causing also the plunger 26 to retract, while source 29 provides for a control bleed off of pressure fluid in cylinder 28 to obtain a constant retaining force.

The embodiments described above show equipment for drawing blanks. The principle of the invention is, however, applicable also to other types of forming processes such as squeezing. The embodiment shown in FIG. 4 illustrates apparatus for direct cold extrusion. The punch 34 illustrated here has a projection with hexagonal cross section, the blank 31 in this case is a tube with hexagonal internal cross section.

That tube has to be placed onto the projecting portion of punch 34. Reference numeral 32 refers to an extrusion die with bottom opening 33.

Punch 34 is provided with a lateral bore 35 adjacent the end of blank 31 facing away from the die. Spring 36 in bore 35 urges a ball 37 radially against one inner side of blank 34, for retaining the blank on the punch. The blank 34 may have a small recess. As blank 31 is slipped over the punch, ball 37 engages the blank at that recess in snap action andretains the blank, at least until engaging the die. As extrusion flow occurs primarily at the lower end of the blank, the retaining device does neither influence the forming process nor is it influenced by it. Generally speaking, snap action type means can be provided to hold a blank or billet remote from the principle areas of flow.

It can readily be seen that the particular type of retaining device employed depends to a considerable extent on the type of punch and upon the contour of the blank. Nevertheless, the retaining device (1) must hold the hollow blank securely on the punch, (2) must move with the punch during operating stroke, (3) does not have to provide any function as soon as the coacting die engages the blank, (4) must not disturb the subsequent working of the blank, and (5) should not be damaged by the deformation of the blank.

The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be included.

We claim:

1. Apparatus for forming cup-shaped hollow blanks each having a bottom, the apparatus including a punch and a die for determining the outer dimensions of the formed product, a cup-shaped blank being slipped on the punch, the punch pressing the blank through the die, the improvement comprismg:

a counter punch traversing the die for retaining a blank on the punch; and

means for positioning the counter punch for forcing the counter punch against the bottom of the blank from the outside in direction opposite to direction of punch movement and in the central area of the bottom only, as being negligibly affected by the forming process, thereby holding the blank on the punch, beginning prior to drawing, the counter punch as rendered efi'ective by the means moving with the punch during operating stroke and at least until the blank is engaged by the die. 2. Apparatus as in claim e means for positioning the counter punch to engage the bottom of the blank through the die, including means to operate the counter punch to recede with progression of the punch, while providing for constant retaining force.

3. Apparatus as in claim 1, the means for positioning including a piston on the counter punch and a piston chamber for the piston, a means for controlling pressure in the piston chamber for the counter punch to recede as the punch advances thereby causing the counter punch to hold the blank on the punch at approximately constant holding force. 

1. Apparatus for forming cup-shaped hollow blanks each having a bottom, the apparatus including a punch and a die for determining the outer dimensions of the formed product, a cup-shaped blank being slipped on the punch, the punch pressing the blank through the die, the improvement comprising: a counter punch traversing the die for retaining a blank on the punch; and means for positioning the counter punch for forcing the counter punch against the bottom of the blank from the outside in direction opposite to direction of punch movement and in the central area of the bottom only, as being negligibly affected by the forming process, thereby holding the blank on the punch, beginning prior to drawing, the counter punch as rendered effective by the means moving with the punch during operating stroke and at least until the blank is engaged by the die.
 2. Apparatus as in claim 1, the means for positioning the counter punch to engage tbe bottom of the blank through the die, including means to operate the counter punch to recede with progression of the punch, while providing for constant retaining force.
 3. Apparatus as in claim 1, the means for positioning including a piston on the counter punch and a piston chamber for the piston, a means for controlling pressure in the piston chamber for the counter punch to recede as the punch advances thereby causing the counter punch to hold the blank on the punch at approximately constant holding force. 